The invention relates to a method for operating a telecommunications system having a switching station and a plurality of internal subscriber stations which are connected to it and with whose aid the switching station can simultaneously operate a limited number of channels of the same or a different type, and to a telecommunications system in which the method can be implemented.
It is advantageous for a subscriber to know the current state of, for example, a cordless telecommunications system. In general, information about the system state is transmitted in the form of signal tones (free tone, busy tone). It is disadvantageous that this information is not received until during or after the setting up of a connection. Furthermore, this information is also not adequate for many applications. This is the case in particular when a plurality of subscriber stations are connected to a switching station in a telecommunications system, which switching station is in turn connected to a plurality of exchange lines, and the switching station has only a limited capacity for simultaneously possible internal and/or external connections. The user who wishes to set up, for example, a connection to another subscriber cannot decide just on the basis of the busy tone whether the dialled subscriber number is currently busy or whether the telecommunications system is overloaded and therefore cannot set up the connection. Furthermore, repeated futile dialling of a subscriber number, after each of which attempts a busy tone can once again be heard, which not only severely stresses the user's patience, but also severely loads the battery in the internal subscriber station. This is further compounded by the load of the environment in which the telecommunications system is located, by radio traffic and by the additional loading of the system itself. This futile dialling must be accepted if the dialled subscriber number is actually busy, but these repeated dialling processes are particularly annoying when caused by overloading of the telecommunications system being used.
The object of the present invention is therefore to provide a method and a device by means of which the previously described disadvantages are overcome, that is to say by means of which a subscriber station and/or the subscriber using this subscriber station is better informed about the system state with regard to overloading of the telecommunications system, and by means of which repeated dialling processes are avoided in which it is impossible for a connection to be set up because the telecommunications system is overloaded.
The achievement of this object is defined in terms of the method in the characterizing part of Patent claim 1, and its achievement in terms of the device is defined in the characterizing part of Patent claim 10, advantageous refinements and developments in each case being located in the subsequent subclaims.
The method according to the invention for operating a telecommunications system having a switching station and a plurality of internal subscriber stations which are connected to it and with whose aid the switching station can simultaneously operate a limited number of channels of the same or a different type is characterized in that the switching station reports to all the internal subscriber stations by transmitting a respective busy signal that a channel of the appropriate type is not available, and each internal subscriber station is changed by the busy signal to a state in which it cannot initiate a connection being set up on the corresponding channel.
The transmission of a busy signal to each subscriber station which is connected to the switching station, when all the internal or external channels are busy, results in the internal subscriber station being signalled as to whether a connection is possible before the process of setting up a connection rather than not until during or after the setting up of a connection. If the setting up of a connection is started, because of this information, only when the system has sufficient free capacity, then, once a connection has been set up, a busy tone is produced only when the dialled destination is actually busy. By changing each subscriber station to a state in which it can no longer initiate a connection being set up in the corresponding channels, this indicates to the user, even before the frequently tedious dialling process, that a connection is currently impossible because of the limited system capacity. Furthermore, this measure saves the energy which is required on each occasion for the redialling in the internal subscriber station. It should also be noted in particular that, as a result of this method, the radio traffic which is required in an overloaded telecommunications system for setting up a line can be considerably limited.
A telecommunications system according to the invention having a switching station and a plurality of internal subscriber stations which are connected to it and with whose aid the switching station can simultaneously operate a limited number of channels of the same or a different type is characterized in that the switching station contains a signal generator which produces a respective busy signal and sends it to all the internal subscriber stations when a channel of corresponding type is not available, and each of the internal subscriber stations contains a blocking device, which can be driven by the respective busy signal and, on reception of the respective busy signal, changes the internal subscriber station to a state in which it cannot initiate a connection being set up on the corresponding channel.
This embodiment according to the invention is particularly advantageous for carrying out the method according to the invention, since the signal generator can thus be contained in the signal-processing circuit section of the switching station, and the blocking device can be implemented by the processor of the internal subscriber station.
The method is furthermore characterized in that the respective busy signal is buffer-stored in each internal subscriber station.
The buffer storage results in the respective busy signal not having to be transmitted continuously to the subscriber stations, and nevertheless permanently being available in the subscriber station in the event of a corresponding busy channel.
According to a development of the method, the various types of channels may be external or internal channels.
This distinction allows a subscriber to distinguish from the start whether he can still receive external or internal connections, since a dedicated busy signal is in each case present for them.
According to another development of the method, the various types of channels may be channels for controlling functions of the switching station.
This advantageous development of the method allows the advantages according to the invention to be available not only for connections between the internal subscriber stations and other internal or external subscriber stations, but also for programming or for calling up special functions of the switching station via the service access or accesses which can be dialled like an internal telephone number.
The method is still further characterized in that the various types of channels are voice channels or data channels.
This advantageous development results in the advantages which the invention offers in addition to normal voice connections, for the use of data connections as well. In consequence, for example, cordless fax units can considerably limit their radio traffic.
The method is also characterized in that, if at least one of the channels becomes free, the switching station sends a respective reset signal to all the internal subscriber stations in order to change them once again to a state in which it is possible for them to initiate a connection being set up on the corresponding channels.
As a result of this advantageous refinement of the method according to the invention, the channel state (the state as to whether the internal or the external voice and/or data channels or the channels for controlling functions in the exchange are or are not busy) does not need to be transmitted and checked continuously, but only when a state change occurs. In order to carry out the method, the actually current information about the channel state is permanently present in the subscriber station in that, after any change in the state, it is transmitted to the subscriber station, is stored there and, when new information arrives, is overwritten by it.
In this case, permanently means that the information which was received at an earlier time is in each case overwritten, and the current state is therefore permanently present. The information is lost when the subscriber station is switched off. This is not disadvantageous since the subscriber station is transmitted the respectively current busy signal or reset signal at the latest when a change in the channel state occurs after it is switched on. In this case, it is also necessary to consider the situation in which the internal subscriber station was not able to record a change in the channel state during the phase when it was switched off and thus information which was stored through the switched-off phase would not be up to date. The current channel state can advantageously be transmitted to the internal subscriber station, from the switching station, in an initialization phase after the internal subscriber station has been switched on.
Another refinement of the method is characterized in that visual or audible indications are driven by the busy signal.
This indication option allows the user to know even before a connection attempt whether he can successfully carry out such an attempt and under some circumstances therefore does not need to initiate this, since the capacity of the telecommunications system has already been exhausted in terms of the desired channel.
The information about channel overloading can be transmitted quickly and clearly to a user by such a visual representation by means of an already existing display on the internal subscriber station or by means of additional light or indication units which are present on the internal subscriber station.
By means of the audible information option, the information about channel overloading is transmitted to the user in the conventional manner, this taking place immediately after lifting the handset, or a corresponding action. This can additionally be done for one of the other indication types, or just for the one. The user therefore does not need to monitor specific indications, for example, even before an attempt to set up a connection, but is informed immediately before then, nevertheless, by the indication of a respective busy signal that it is impossible to set up a connection on a corresponding channel. This can be done by the acoustic presentation of the channel information itself or by a cue to look at the visual indications.
Yet another development of the method is characterized in that, a connection which corresponds to a dialled number which is stored in the internal telephone is automatically set up via a channel when the internal subscriber station receives the reset signal for this channel.
By such automatic redialling without involving lines or radio channels, the user is saved having to activate the redialling, and the system is not loaded by pointless redialling attempts to the internal subscriber stations which are connecting to the switching station. If the system load permits a renewed dialling attempt, then all the internal subscriber stations are informed of this and a station whose user wishes to set up a connection can do so immediately and automatically without having to start a futile connection setting up process at specific time intervals. This advantageous refinement of the invention provides a redialling option which, while saving a considerable amount of energy and while maintaining all the advantages which have already been mentioned above in the internal subscriber station, provides the quickest possible possibility for successful redialling.
A further refinement of the method according to the invention is characterized in that radio channels are used at least as internal channels.
A telecommunications system according to the invention is advantageously characterized in that each internal subscriber station contains a memory device for storing the respective busy signal.
Said telecommunications system is furthermore characterized in that each internal subscriber station contains a reset circuit for erasing the respective stored busy signal, and the reset circuit can be driven by a respective reset signal from the switching station which produces the respective reset signal if at least one of the corresponding channels becomes free, and sends said reset signal to all the internal subscriber stations.
Yet another advantageous refinement of a telecommunications system according to the invention is characterized in that each internal subscriber station contains visual or audible indication devices which can be switched on and off corresponding to the respective busy signal for each group of channels.
Finally, a telecommunications system according to the invention is characterized in that the internal subscriber stations are radio telephones, cordless telephones, cordless fax units or other devices for remote data transmission.